In the fabrication of semiconductor devices such as integrated circuits, memory cells, and the like, a series of manufacturing operations are performed to define features on semiconductor wafers (“wafers”). The wafers include integrated circuit devices in the form of multi-level structures defined on a silicon substrate. At a substrate level, transistor devices with diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define a desired integrated circuit device. Also, patterned conductive layers are insulated from other conductive layers by dielectric materials.
During the series of manufacturing operations, the wafer surface is exposed to various types of contaminants. Essentially any material present in a manufacturing operation is a potential source of contamination. For example, sources of contamination may include process gases, chemicals, deposition materials, and liquids, among others. The various contaminants may deposit on the wafer surface in particulate form. If the particulate contamination is not removed, the devices within the vicinity of the contamination will likely be inoperable. Thus, it is necessary to clean contamination from the wafer surface in a substantially complete manner without damaging the features defined on the wafer. However, the size of particulate contamination is often on the order of the critical dimension size of features fabricated on the wafer. Removal of such small particulate contamination without adversely affecting the features on the wafer can be quite difficult.
Conventional wafer cleaning methods have relied heavily on mechanical force to remove particulate contamination from the wafer surface. As feature sizes continue to decrease and become more fragile, the probability of feature damage due to application of mechanical force to the wafer surface increases. For example, features having high aspect ratios are vulnerable to toppling or breaking when impacted by a sufficient mechanical force. To further complicate the cleaning problem, the move toward reduced feature sizes also causes a reduction in the size of particulate contamination that may cause damage. Particulate contamination of sufficiently small size can find its way into difficult to reach areas on the wafer surface, such as in a trench surrounded by high aspect ratio features or bridging of conductive lines, etc. Thus, efficient and non-damaging removal of contaminants during modern semiconductor fabrication represents a continuing challenge to be met by continuing advances in wafer cleaning technology. It should be appreciated that the manufacturing operations for liquid crystal displays (i.e., flat panel displays) suffer from the same shortcomings of the integrated circuit manufacturing discussed above.
Cleaning methods that use multi-phase cleaning solutions (i.e., foam, emulsions, etc.) that are comprised of a dispersed phase, continuous phase and solids overcome many of the problems associated with conventional wafer cleaning methods. When a force is applied against the multi-phase cleaning solution, the solids dispersed within the continuous phase come into contact or interact with the particulate contaminants on the wafer surface. As the cleaning solution, with the solids, is removed from the wafer surface the particulate contaminants are also removed.
There are several inherent challenges with using multi-phase cleaning solutions to clean wafer surfaces. One is that it is difficult to ensure that the solution is uniformly applied across the entire wafer surface. Uneven application of the solution may result in an uneven cleaning profile on the wafer surface due to non-uniform rinsing of the wafer surface. Another is that it is difficult to uniformly apply force against the solution across the wafer surface so that the embedded solids actually come into contact with the contaminant particulates during cleaning. As discussed earlier, the solids must come within the vicinity of the contaminant particles before they can interact and effectuate the removal of the particles.
In view of the forgoing, there is a need for an apparatus and method for uniformly applying a multi-phase cleaning solution (i.e., foam, emulsions, etc.) across a wafer surface during the cleaning of the wafer surfaces.